The present invention relates in general to mine roof or rock bolt expansion anchors, and more particularly to an improved mine roof or rock bolt expansion anchor provided with means for quickly initially expanding the same in a mine roof bore hole to achieve initial anchorage for further manipulation to properly anchor it in place, and wherein the anchor is formed with a shell and bail composed of a uniform thickness of one piece of metal activated by a cone nut threaded onto a bolt to expand the shell into contact with the rock of the bore hole wall.
Roof suspension bolts or, as properly called, mine roof bolts, are now widely used. In the use of these bolts, holes are drilled upwardly into the mine roof or ceiling or into the overhanging rock mass, in a mine or similar excavation, and supporting bolts, designed to be secured in the bore holes to exert compressive force against the roof or to be directed through supporting plates or bars engaged with the roof or ceiling, are inserted in the holes and anchored therein for securely supporting the portions of the mine roof or ceiling near the bolts. The anchoring of the bolts is effected by employing an expansion anchor, inserted into the roof bores and through which the bolts are threaded. Means are included in these expansion anchors which are effective upon threading of the bolts inwardly to a predetermined extent to expand the shell portion of the anchors and cause them to firmly grip the wall portions of the bolt receiving bores. It is the purpose of the present invention to provide a novel form for such a mine roof or rock bolt expansion anchor which can be easily and economically manufactured, and which is subject to being inserted into a receiving bore formed in the rock ceiling or roof with great facility and capable of very securely anchoring a bolt threaded therethrough.
Such mine roof bolts as previously known usually consist of a long bolt provided with a multi-part permanent anchoring means on one end of the bolt to be expanded into secure retaining engaement with the side walls of the upper portion of a hole drilled in the roof of a deep mine, rock or other excavation. The anchoring means of conventional mine roof bolts presently in use are expandable, usually by manually driving the bolt with an appropriate bolt rotating tool. A problem involved in the installation of conventional mine roof bolts resides in the fact that such bolts are inserted in a substantially vertical hole in the roof or ceiling of a mine passageway, and many mine roof bolts do not have provision for quickly achieving initial expansion to temporarily restrain the bolt in place, after it has been inserted to its full extent in the drilled hole in the mine roof, and consequently, difficulty is encountered in holding the bolt temporarily in the hole while sufficient torque is applied to the bolt to expand the anchor to permanent anchoring condition. It is rather difficult and requires a great deal of care on the part of a laborer to manually hold the bolt in place during the period required to manipulate an appropriate tool to expand the expandable anchoring means so that it reliably retains itself in place in the hole.
An object of the present invention, therefore, is the provision of a novel form of mine roof or rock bolt expansion anchor of the bail type which can be easily and economically manufactured, which is convenient to operate, and which is capable of providing highly reliable anchoring of a bolt in a hole formed in a mine roof or rock ceiling or the like.
Another object of the present invention is the provision of a novel expansion bolt anchor of the bail type for mine roofs or similar installations formed so that the anchor will expand at a more rapid rate during initial turning of the bolt after the unit is placed within the bore hole and thereby achieve fast initial anchorage and which then expands at a slower rate upon further turning of the bolt, facilitating installation of the expansion anchor and providing highly reliable anchorage capacity.
Another object of the present invention is the provision of a novel expansion bolt anchor for mine roofs or ceilings and like installations, having high total anchorage capacity, wherein the anchor shell is designed with two opposing leaves permitting utilization of raw material which can be conveniently purchased in coil form, minimizing the cost of shearing of the raw material and the cost of handling the raw material when compared to the use of individual strips, thereby offering a most economical method for production of the unit without welds or mechanical attachment of a bail to the shell which might break off or distort in production.
Another object of the present invention is the provision of a novel expansion bolt anchor for mine roofs or ceilings and the like to be inserted in bore holes formed in the rock or roof formation, wherein a cone nut is provided to be threaded on the bolt to be anchored in the bore hole and drawn between opposite substantially semi-cylindrical leaves of an expandable shell formed initially as a one piece blank from a flat coil of metal raw material with the two leaves of the shell interconnected by a bail having a circular top which is slightly cupped in manufacture and includes a pop-out portion which is designed to break away under a specified load when the end of the bolt is driven against the pop-out portion with sufficient load during advancement of the bolt to fix the bolt anchoring assembly in the bore hole.
Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating a preferred embodiment of the invention.